Like almost all machinery with moving parts grinding together, refrigeration equipment needs proper lubrication to operate. Good lubrication with clean oil can maintain a refrigeration compressor in service for extended periods with little other maintenance. A poor oil quality can cause continual problems, some of which may go unnoticed until the equipment has a catastrophic breakdown.
Unlike other machinery, such as a car engine, however, the oil in a refrigeration system cannot practically be changed every two months to assure a clean system. The reason is related to ozone depletion. Each time refrigeration equipment is opened or purged there is some release of refrigerant, usually CFC, to the atmosphere. This has been linked to the alarming decimation of the earth's ozone layer--the once thick blanket of O.sub.3 which helps to filter out harmful components of the sun's rays. Thus lubrication maintenance for refrigeration systems has evolved to its own unique process.
Historically, the oil used to lubricate and cool the moving parts in refrigeration equipment, such as chillers, has been drained and replaced annually. The service branch of the equipment manufacturer would haul away and dispose of the used oil as would other outside service vendors. More recently, individuals and companies have frequently paid a fee as a built-in cost in a service contract to have their waste oil hauled away. Some of the oil was reclaimed, after which it could then be resold, usually as a lower grade oil.
However, changes are rapidly taking place in the industry. It is becoming increasingly difficult as well as costly to arrange for disposal of the oil. Great concerns have been raised by various government agencies regarding such oil as a hazardous waste. More alarming is the anxiety created by the release of harmful refrigerants into the atmosphere each time the seal is broken on these refrigeration devices. Most notably is the low pressure centrifugal type equipment which uses R-11 refrigerant. Those still using the machinery continually face fines for the release of R-11 above a certain mandated amount. It is believed that literally hundreds of thousands of these offenders exist.
The present invention has sought to address these problems in the low pressure centrifugal type refrigeration equipment. And in fact, the present invention has sought to anticipate further restrictions and problems linked to pending legislation which may reduce the limits for release of R-11 into the atmosphere.
In understanding the nature of the problem addressed, it is essential that a distinction be made between the low pressure class of equipment and their heavily legislated high pressure counterparts. Because the low pressure class of systems have presented far less safety risks in the industry they have been almost unrestricted in their use. On the other hand, equipment classified as high pressure has evolved under continuous restriction. The high pressure class of equipment is forced to meet countless ASHRAE/ASME/ANSI/ASTM codes. This of course increases the cost of the refrigeration equipment dramatically. High pressure centrifugal equipment requires more KW per ton of cooling than its counterpart (low pressure), and is dramatically more dangerous to operate. Maintenance costs are higher for the high pressure vessels, and the operating staff must be more specialized than those operating the low pressure machines. Perhaps a key difference is that the high pressure machine has no vacuum on the low side line and is generally tested at between 300 pounds per square inch (psi) to 600 psi. The result of this greater-than-atmospheric pressure internally is that air does not leak into the equipment during operation. Atmospheric leaks into refrigeration equipment are instrumental to mechanical degradation, and particularly harmful to the lubricating oil. When high pressure machines are tight and properly evacuated at start-up or after service, internal moisture does not become a factor in their operation. For this reason, high pressure machines do not have, or need, an automatic purge cycle to keep air out of the system.
Conversely, low pressure equipment, the focus of the present invention, has been much less regulated. Presently it does not have to meet the regulations set forth by the higher pressure vessels. These machines are generally tested at 30 psi and operate under 15 psi. They may reach 15" (Hg) of vacuum on the low (suction) line side, and even lower during evacuation of the filter housing. Typically, the low pressure machine is about 35% larger than high pressure centrifugal equipment. Depending on internal and external conditions, while the machine is in its idle off-state, the equipment will assume a negative pressure internally. This negative pressure state constantly has the potential of allowing air to leak into the system. Each leak is the possible propagator of catastrophic failure. As the temperature falls inside the machine the water vapor within the atmosphere condenses into droplets on the metal surfaces. The water in turn reacts with other contaminants to produce acids that may break down motor windings and erode metal surfaces. To help counter-act this problem, those skilled in the art have utilized a purge pump. The pump automatically starts when air or water is present in the purge system and stops when the air and/or water has been removed. Not only does this pump push the air out of the machine, but a significant amount of the refrigerant leaves as well. The process of the present invention traps the water, thus reducing the amount of run time of the purge pump and thus reducing the amount of R-11 pumped into the atmosphere.
These distinct differences between high and low pressure refrigeration equipment have led those skilled in the separate arts to address very different problems. To these persons skilled in the representative arts, what generally applies to one, such as internal equipment leaks in low pressure, does not necessarily apply to the other. Furthermore, while the use of the purge pump system addresses the problem of water contamination in a low pressure system, it does so at the cost of more important environmental concerns.
Ancillary to the high vs. low pressure classification is the distinction between refrigeration equipment types. In the field there exists centrifugal type equipment, as shown in U.S. Pat. Nos. 4,404,812 to Zinsmeyer, 4,032,312 to Anderson, 3,650,634 to Osborne et al., and 3,163,999 to Ditzler et al., and piston and screw type equipment, as shown in U.S. Pat. No. 4,586,875 to Aman, Jr. (piston type compressor). The latter two types are strictly high pressure class equipment with very different lubrication and operational concerns, while centrifugal type equipment can be either low pressure or high pressure. The present invention focuses on the low pressure centrifugal type equipment.
Some of the major problems inherent to low pressure, centrifugal type refrigeration equipment are water caused by condensation, and water due to leaks in the oil cooler system. As this water mixes within the system it forms hydrochloric acid (HCl), an extremely caustic acid. The acid tends to degrade the system by destroying internal parts. Several devices, such as that disclosed in U.S. Pat. Nos. 4,975,188 to Brunsell et al., 4,830,745 to van der Meulen, 4,687,572, 4,591,433, and 4,534,860 all to Budzich, teach the removal of water from lubricating oil, but the oil must first be removed from the lubricating system. These particular devices are called centrifugal type separators, not to be confused with centrifugal type refrigeration equipment. The separators subject the oil/water mixture to high velocity centrifuging to obtain separation of the various liquids. The water is then drawn off to leave just the oil. Separators of this type are not well suited for use in refrigeration equipment because of their size--they are typically suited for large volume separation--and cost.
In U.S. Pat. Nos. 3,208,596 to Gravert and 4,892,667 to Parker III, et al., water removal is taught in lubricating oil systems using coalescing filters. This procedure consolidates tiny water droplets into larger water droplets which, when they reach a certain size, may be removed by gravity. Gravert uses hydrophobic screen separators (10 microns average opening size) to block the passage of any water droplets, while still allowing the passage of oil. The very size of the coalescing apparatus does not make it a practical solution to the water problem in low pressure centrifugal refrigeration equipment.
Somewhat related to the problem of water contaminants is that of minute or submicron particles. As these tiny contaminants build up in any type of machinery they can cause great wear and tear on the moving parts. In full flow filtering systems, submicron filtering is not achievable because of the necessary retention needed to be effective. Longer retention of the oil in these full flow systems would naturally cause the lubrication system to be starved of oil, or perhaps require an impractical amount of surplus oil to operate. Thus, bypass filters have been used to provide submicron filtering for smaller portions of the oil supply. After several passes through the bypass system as much as 98% of these submicron particles can be removed. However, in low pressure centrifugal refrigeration equipment one is presented with the problem of sufficient filtering due to a positive pressure inlet side and a negative pressure on the low (suction) side. Under these circumstances the oil has a tendency to exit the filtering unit without being adequately retained for effective filtration. Those having representative skill in the art have not recognized the benefits of balancing the operating parameters of the filtering system to sufficiently filter oil at a submicron level without starving the lubrication system. Attempts have been made to control the inlet portion of oil, but efforts have fallen short of metering the return of filtered oil. This is particularly true for newly established equipment which has no guidelines to follow for setting these parameters correctly. The present invention is designed to allow careful balancing of the essential operating parameters to provide a reliable oil filtering system on both existing and new systems.
One of the most difficult situations faced by those using the low pressure centrifugal refrigeration equipment is the need to shut down the equipment for routine filter and oil changes. The process can involve several hours of discontinued operation of the equipment. Due to the considerable cost involved there is little redundancy in the field of cooling apparatus (i.e., use of backup systems). Shutting a cooling system down for even a short period of time can cause a considerable amount of inconvenience. Yet all known devices require discontinued operation of the refrigeration system to carry out a routine maintenance procedure such as changing the oil filter. Perhaps surprisingly, those skilled in the art did not realize that it would be possible to isolate the filtering system entirely, thereby permitting continued operation of the lubricating system and therefore continued operation of the refrigeration equipment during routine oil and filter changes. Certainly bypass filter systems have been known for some time. However, one which allowed the filter to be changed without discontinuing operation of the equipment had not, until the present invention, been available in refrigeration systems.
Environmentally, the main concern however, with shutting down the machine is more the release of CFC's into the atmosphere. As alluded to earlier, there are numerous government agencies which have sought to impose stiff penalties on R-11 users. With the annual release of R-11 into the atmosphere by approximately 500,000 low pressure centrifugal type refrigeration systems, the environmental impact becomes quite alarming. Such dangers of refrigerant release into the atmosphere are well documented in U.S. Pat. Nos. 4,805,416 to Manz et al., 4,261,178 to Cain, 4,110,998 to Owen, 3,699,781 to Taylor, 3,145,544 to Weller, and 2,341,429 to Elsey. The present invention would require less frequent maintenance to replace degraded lubrication oil. It is anticipated that oil changes could be performed every five years, rather than the standard one year. These changes could be coincided with the specification check-ups which are performed every five years as well. Theoretically the reduction of R-11 released into the atmosphere each year would be 80%. The key to this practice would be to maintain the oil in a suitable lubricating state, without degradation due to contaminants.
The present invention, in both its apparatus and methods, recognizes and addresses these problems and overcomes the limitations perceived by those skilled in the art by presenting a design which, among other aspects, allows for the removal of water, glycol and submicron particles without having to shut down the refrigeration system. Those skilled in the art of low pressure centrifugal refrigeration equipment design have long been aware of these problems of water degradation of oil, submicron particle impurities, and environmental contamination. Millions of dollars have been spent to date in both research and fines by those using low pressure centrifugal equipment. All the while the necessary arts and elements for implementing the disclosed invention have existed for sometime. The various patents cited show substantial attempts by those skilled in other fields to solve each of the above problems separately as they exist in their particular art. That is, some have been able to remove submicron particles from lubricating oils, others have accomplished water removal by oil reclamation or by use of the standard purge pump, and still others have addressed the environmental concerns. However, a system which integrates these capabilities into the permanent filtering system of low pressure centrifugal type refrigeration equipment has not existed until the present invention. Instead of understanding the true problem, manufacturers have coped with the inherent limitation to some of these devices and methods, such as the purge pump. There appeared to be a failure to fully understand the problems and impacts of properly filtering lubricating oil in low pressure centrifugal type refrigeration equipment.